This is an integrative research effort to understand and define basic mechanisms of tolerance. Individual projects are organized to define processes regulating induction and maintenance of immunologic unresponsiveness to self-antigens. The unifying theme of this program is that tolerance is a complex process in which the inherent responsiveness of immune cells as well as anatomic influences and interactions between B and T cells play pivotal roles in determining responsiveness to self and pathogen-associated antigens. As such, attempts to understand tolerance at the mechanistic level must consider this complexity utilize experimental systems that facilitate definition of tolerance mechanism within the context of this complexity. The program proposed will accomplish this by bringing together individual investigators with demonstrated expertise in defining the complexity of immunoregulation and a research commitment to understanding mechanisms of tolerance. Each of the laboratories involved has specific expertise in B and T cell immunobiology and how these cells interact with one another and with other immune system moieties. In Projects 1 and 4, an innovative new technology will be used to allow definition of cellular and molecular processes within complex in vitro cultures that model the in vivo process of tolerance and activation. In Project 2, a newly discovered molecule associated with anergic T cells will be exploited to isolate these cells from complex ex vivo populations and then define the molecular basis of T cell anergy. Project 3 exploits a new finding that B cells are necessary for the breech of T cell tolerance that accounts for autoimmunity in the NOD mouse. Adoptive transfer of specific cellular components involved in the autoimmune reaction will allow the definition of the cellular basis for induction of autoimmune diabetes in this mouse model. The principal investigators involved with these projects have a long history of scientific interaction that they wish to maintain and expand through the successful funding of this application.